1. Field of the Invention
The present invention relates to motor vehicle cabin climate control and more particularly to interoperative, easily maintained cabin and engine compartment modules, which are used to implement cabin heating and cooling in an efficient and reliable manner.
2. Description of the Problem
Combined systems for heating, ventilation and air conditioning (HVAC) have become an industry norm for automobiles and trucks. Among the features common to most if not all such systems are, a heater core, a blower to force air through the heater core, an evaporator for cooling air, distribution duct work, and a plurality of flow directing doors controlling the source of intake air, the route of the air through the system and the distribution points of the air into the cabin. The construction, arrangement, packaging and control of these elements has a number of ramifications for unit efficiency, cost and ease of manufacture and maintenance, space requirements for installation and passenger comfort.
Passenger cabin heating and windshield defrosting is provided by forcing air through interstices in a heater core, which, in vehicles with liquid cooled engines, use circulating engine coolant as a source of heat. Contemporary HVAC systems often provide no cutoff valve for interrupting coolant circulation through the core. Instead, internal air flow control doors cut off the core from air circulation when heat is not desired. Coolant cutoff valves have proven relatively unreliable in many applications, and eliminating them has produced maintenance savings. Heater cores themselves are an occasional maintenance problem, being prone to corrosion and leakage with long term use. The positioning and manner of installation of heater cores has made them difficult to replace.
Combined heating, ventilation and cooling systems have been adopted to reduce the costs of duct work, since only one set of distribution channels is required. Such an arrangement, combined with the absence of a heater core cutoff valve, contributes to greater complexity in the arrangements for air flow control. Rapid cooling of the vehicle passenger compartment when a vehicle is first turned on is often achieved by recirculating cabin air rather than drawing in outside air. Some defogging regimens call for both cooling the air, to remove moisture, and heating the air to clear interior surfaces of the vehicle greenhouse. Flow control doors must be positionable to draw air from either outside or inside the passenger compartment, to direct air through either or both the heater core and the evaporator and then to mix the air before it is directed against the glass. Finally, vent doors must provide for distribution of air to the desired locations. Kinematic positioning movements control the position of various vent and flow control doors and to deliver adequate air flow to the desired zone.
Individual products of the motor vehicle industry are frequently sold world wide. What were once considered North American trucks have found markets in South America, Australia and South Africa, among other places. Australia and South Africa use right hand drive vehicles and an HVAC system intended for a vehicle to be sold in both left hand and right hand drive countries can cost less in tooling if the components fit either type of vehicle.